Respiratory systems provide breathable gas, such as oxygen, anesthetic gas and/or air directly to a patient's mouth, nose or airway to assist or facilitate breathing by the patient. A ventilator may be used as part of the respiratory system to drive the breathable gas to the patient through an inspiratory limb hose or conduit. An expiratory limb hose or conduit may be provided to carry expelled air and other gas(s) from the patient back to the ventilator or to atmosphere.
It is typically desired to warm and impart humidity to the breathable gas before it is provided to the patient. For that purpose, many respiratory systems include a humidification system including a heater unit and a disposable water chamber adapted to be heated by the heater unit. The heater unit supports a hot plate heater, which may be comprised of one or more heating elements and a metal plate defining a hot plate. The heater unit also typically houses the necessary electrical and electronic components to regulate the temperature of the heater as well as heating circuits of the inspiratory and/or expiratory limbs of the breathing circuit. A wall of the chamber, such as the bottom surface thereof, is thermally conductive. The chamber is removably supported on the heater unit with the bottom surface in thermal contact with the hot plate of the heater to thus heat the water in the chamber. The chamber may be manually refillable, or there may be a water source to selectively fill the chamber as it empties. The breathable gas is coupled to the chamber, and is passed through the chamber to be heated and humidified. The inspiratory limb carries the heated and humidified gas to the patient. Examples of heater units, chambers and vented water supplies are shown in U.S. Pat. Nos. 6,988,497 and 5,943,473; and co-pending U.S. patent application Ser. No. 11/469,086 filed Aug. 31, 2006 and Ser. No. 11/469,113 filed Aug. 31, 2006.
The hot plate is typically a thick machined or cast metal member so as to have a significant thermal mass. Such thick metal members can be costly and can be undesirable for other reasons. Moreover, the hot plate heater is typically mounted to the heater unit by fastening mount members, such as spring loaded metal screws connected to an underlying support structure of the heater unit. Assembly of such hot plate heaters to the heater unit can be time-consuming and costly. Moreover, the mount members can conduct heat away from the hot plate thereby undesirably reducing thermal efficiency. In some situations, the underside or lower edge of the hot plate may be undesirably exposed to air further reducing thermal efficiency such as due to convection losses.